Vehicle exterior materials or cellular phone housings are often exposed to low-temperature environments during use and are readily exposed to light sources such as ultraviolet rays. In addition, these materials require high heat resistance to endure hot sunlight and high tensile strength.
Products utilizing, as a main resin, a polycarbonate resin having superior heat resistance, dimensional stability and tensile strength have been developed so as to provide resin compositions satisfying these properties.
However, polycarbonate resins are disadvantageously readily brittle due to poor low-temperature impact strength and room-temperature impact strength. Accordingly, an attempt to improve impact strength using a rubber-reinforced thermoplastic resin as an impact reinforcing agent has been made.
General rubber-reinforced thermoplastic resins include acrylonitrile-butadiene-styrene (ABS) resins, acrylonitrile-styrene-acrylonitrile (ASA) resins, methyl methacrylate-butadiene-styrene (MBS) resins, acrylic impact modifier (AIM) resins and the like. These resins utilize a rubber polymer having a glass transition temperature of 0° C. or less as a core and a shell layer selected in consideration of compatibility with a matrix resin is produced through graft copolymerization.
In general, ABS resins prepared by graft copolymerizing a butadiene rubber polymer with styrene and acrylonitrile monomers have impact resistance, processability, beautiful appearance, superior mechanical strength and high heat deflection temperature and are thus utilized in a variety of applications such as vehicle components, electronic and electrical products and constructional materials.
However, ABS resins are readily oxidized by ultraviolet rays, light and heat in the presence of oxygen, are changed in appearance and color and have a drawback of deteriorated mechanical properties due to presence of ethylenically unsaturated polymer in a butadiene rubber used as an impact reinforcing agent, thus being disadvantageously unsuitable for use as outdoor materials.
Accordingly, in order to obtain thermoplastic resins having superior physical properties as well as excellent weather resistance and aging resistance, an ASA resin which is an acrylate-styrene-acrylonitrile terpolymer utilizing an acrylic rubber free of an ethylenically unsaturated polymer is used as an impact reinforcing agent, instead of a butadiene rubber. Such an ASA resin is utilized in a variety of applications including electronic and electrical components, constructional materials, vehicles, ships, leisure products and gardening materials for outdoor use.
ASA is generally prepared as multilayer copolymer graft particles, that is, core-shell structures. An acrylic rubber for improving impact resistance is generally used as the core and styrene, acrylonitrile, methyl methacrylate or the like for improving colorability and dispersibility with a matrix resin is generally used as the shell.
However, when an ASA impact reinforcing agent is added to a commonly used polycarbonate (PC), low-temperature impact strength may be slightly deteriorated. Accordingly, in an attempt to improve low-temperature impact strength, an amount of added ASA has been increased. However, this attempt causes deterioration in other property such as tensile strength. Thus, there is a need for acrylate-styrene-acrylonitrile resins which are capable of improving low-temperature impact strength while not deteriorating other properties.